Precipitated silica product, dentifrices containing same, and processes

ABSTRACT

Precipitated silica comprising porous silica particles having a cumulative surface area for all pores having diameters greater than 500 Å of less than 8 m 2 /g, as measured by mercury intrusion, and a percentage cetylpyridinium chloride (% CPC) Compatibility of greater than about 55%. The precipitated silica product is especially well-adapted for use in dentifrices containing cetylpyridinium chloride, which do not attach to the low surface area silica product in a meaningful level and thus remain available for antimicrobial action. Processes for making the silica product are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of prior U.S. patentapplication Ser. No. 10/366,604, filed Feb. 14, 2003 now U.S. Pat. No.6,946,119, which is hereby incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to precipitated amorphous silica, and processesfor making it. The precipitated silica is especially well-adapted foruse in dentifrices containing cetylpyridinium chloride.

2. Description of the Related Art

Modern dentifrices often contain an abrasive substance for controlledmechanical cleaning and polishing of teeth, and optionally a chemicalcleaning agent, among other common ingredients, such as humectants,flavors, therapeutic ingredients, such as an anticaries agent, rheologycontrol agents, binders, preservatives, colors, and sudsing agents,among others. Oral care products also often contain therapeutic agents,such as anti-microbial agents. Cetylpyridinium chloride (“CPC”) is ananti-microbial agent used for this purpose, such as in mouthwashes andtoothpastes. There is an increased desire among dentifrice manufacturersto incorporate anti-microbial agents in dentifrice applications for thecontrol of malodor and/or other therapeutic action, with CPC being oneof the more favored. It is cost effective and generally recognized assafe. By contrast, some alternative anti-microbial agents currentlybeing used in dentifrices have come under increasing scrutiny forpossible contribution to the increased resistance of some bacterialstrains to antibiotics. CPC is not considered to contribute to thishealth problem.

CPC is a cationic (“positively”) charged compound. CPC's antimicrobialaction is generally understood to result from its ability to bind toanionically (“negatively”)-charged protein moieties on bacterial cellspresent in the mouth. This CPC attachment mechanism results in adisruption of normal cellular function of bacteria and contributes tothe prevention of plaque formation and other bacterial actions.

A problem encountered in CPC usage in dentifrices has been that CPCtends to indiscriminately bind to negatively-charged surfaces. Inparticular, co-ingredients of toothpaste formulations havingnegatively-charged surfaces also may bind to CPC before it performs anyantimicrobial action. Once bound to these nontargeted surfaces, the CPCis generally unavailable to perform any meaningful antimicrobial action.

In this regard, silica is often used as an abrasive in dentifrices. Forinstance, silica's abrasive action is used for pellicle removal fromteeth. Most conventional silicas used in dentifrices havenegatively-charged surfaces. Consequently, CPC adsorbs onto suchconventional silica powders. For reasons explained above, the adsorptionof CPC upon silica or other co-ingredients of the dentifrice is highlyundesirable.

U.S. Pat. No. 6,355,229 describes a CPC compatible dentifriceformulation containing guar hydroxypyropyl-trimonium chloride. The guarcomplex has a higher affinity toward binding to negatively-chargedspecies. It preferentially binds to anionic components leaving CPC freeto bind to plaque.

U.S. Pat. No. 5,989,524 describes a silica that is compatible withflavors obtained by treating the surface of the silica originating fromthe reaction of an alkali metal silicate with an inorganic or organicacidic agent with the aid of an organic compound capable of developinghydrogen or ionic bonds with the Si—OH silanol groups or the SiO⁻anionic groups at the silica surface. The organic agent can be added tothe silica in the form of slurry before or after salts are removed, orcan be sprayed on to dry silica.

A number of patent publications describe processes for making compositesynthetic silica particles, including the following.

U.S. Pat. No. 2,731,326 describes a process of preparing xerogels inwhich a silica gel is stabilized so that the pores of the gel do notcollapse upon drying. It involves a two-stage precipitation processwhere in the first stage silica gel is formed, and in the second stage alayer of dense amorphous silica is formed over the gel particles inorder to provide sufficient reinforcement such that the pores do notcollapse upon drying. The gel particles have a particle size in therange of 5 to 150 millimicrons (nm), and preferably have an averagediameter of from 5 to 50 millimicrons. The resulting reticulatedparticles can be dewatered and dried into powder form. The '326 patentstates that when silica particles have a specific surface area ofgreater than 200 m²/g, it is preferred to replace the water with anorganic liquid, and then dehydrate the silica particles. The '326 patentdescribes silica products with preferred specific surface areas 60 to400 m²/g. The '326 patent indicates little advantage is obtained incarrying the process of accretion to an extreme. The preferred productsof the '326 patent process of accretion are limited so that the originaldense ultimate units of the aggregates do not lose their identity andthe original aggregates structure is not obscured.

U.S. Pat. No. 2,885,366 describes a process used to deposit a denselayer of silica over particles other than silica.

U.S. Pat. No. 2,601,235 describes a process for producing built-upsilica particles in which a silica sol heel is heated above 60° C. tomake nuclei of high molecular weight silica. The nuclei is mixed with anaqueous dispersion of active silica made by acidulating alkali metalsilicate, and the mixture is heated above 60° C. at a pH of 8.7 to 10,such that active silica accretes to the nuclei.

U.S. Pat. No. 5,968,470 describes a process to synthesize silica havingcontrolled porosity. It involves the addition of silicate and acid to asolution of colloidal silica with or without an electrolyte added(salt). The porosity can be controlled based upon the amount ofcolloidal silica added in the first step of the reaction. Silica withBET surface areas ranging from 20 to 300 m²/g, CTAB specific surfaceareas from 10 to 200 m²/g, oil absorption (DBP) ranging from 80 to 400m²/g, pore volumes from 1 to 10 cm³/g, and mean pore diameters from 10to 50 nm could be synthesized. The intended use of materials produced bythis process is in the paper and catalysis marketplace.

U.S. Pat. No. 6,159,277 describes a process for the formation of silicaparticles with a double structure of a core of dense amorphous silicaand a shell of bulky amorphous silica. A gel is formed in a first step.The gel is then aged, wet pulverized, and then sodium silicate is addedin the presence of an alkali metal salt in order to form amorphoussilica particles on the surface of the milled gel particles. Theresultant double structure silica material has an average particlediameter of 2 to 5 micrometers and a surface area of 150 to 400 m²/g.The resultant material is said to have improved properties for use in asa delustering agent in paint and coatings.

Patent publications that describe use of silicas in dentifrice or oralcleaning compositions include the following.

U.S. Pat. No. 5,744,114 describes silica particles adopted forformulation into dentifrice compositions having a unique surfacechemistry as to be at least 50% compatible with zinc values, and have anumber of OH functions, expressed as OH/nm², of at most 15 and a zerocharge point of from 3 to 6.5. The '114 patent describes a process ofpreparing silica particles by the reaction of silicate with an acid toform a suspension or gel of silica. The gel/suspension is thenseparated, washed with water and treated with acid to adjust the pHbelow 7.

U.S. Pat. No. 5,616,316 describes silica that is more compatible withcustomary dentifrice ingredients. In addition to many other ingredients,cationic amines are mentioned.

Another problem associated with usage of conventional silicas indentifrices is that they often have flavor compatibility problems. Thatis, the conventional silicas tend to interact with flavorants includedin the same dentifrice in a manner that creates off-flavors, making theproduct less palatable. This off-flavor problem accompanying use of someconventional silicas in dentifrices is highly undesirable from aconsumer satisfaction standpoint.

A need exists for silicas that can be used together with anti-microbialagents such as CPC in oral cleaning compositions such as dentifriceswithout impairing the respective functions of either ingredient. Silicasthat are more flavor compatible are also in need. In general, the silicadisclosed in this invention may be useful whenever it is desirable tolimit the interaction of the silica particulate with desirable additivesand components found in dentifrice formulations. The present inventionmeets these needs and others as will become readily apparent from thedisclosure that follows.

SUMMARY OF THE INVENTION

This invention relates to a unique silica product comprising silicaparticles that have been surface-modified in a beneficial manner. Thissilica product is particularly useful in dentifrice compositionscontaining cetylpyridinium chloride (“CPC”) or other therapeutic agents.CPC does not appreciably bind to these silica products. Therefore, whencontained in a dentifrice composition, an increased amount of CPCremains available for its antimicrobial duties while the silica abrasiveremains unimpaired by CPC attachment, and it is able to provide themechanical cleaning and polishing action desired from it as an abrasivesilica product. Additionally, the silica product is highly compatiblewith many commonplace dentifrice flavorants. The silica product ofembodiments of this invention reduce the possibility of off-flavors whenpresent together with flavorants. Also, the silica product is highlycompatible with fluoride ion sources such as sodium fluoride. The silicaproduct does not adversely interact with or impair those anticariesagents or their function.

The silica product of embodiments of this invention may be produced viaa process including steps of providing porous silica substrate particlesas a pre-formed material or forming it in-situ, followed byprecipitating active silica upon the silica substrate particleseffective to satisfy the pore size distribution requirements describedherein. In one embodiment, a dense silica material is deposited on thesilica substrate particles effective to penetrate into and/or block atleast part of the pore openings on the silica substrate particles toreduce the pores having a size greater than about 500 Å effective tolimit the cumulative surface area for those sized pores on thesurface-treated silicas to less than approximately 8 m²/g, as measuredby mercury intrusion porosimetry. Experimental results reported hereinreveal that pores sized greater than about 500 Å are more accessible toCPC intrusion than pores having smaller sizes. Consequently, it has beendiscovered that the reduction of pores on the silica particles havingsizes of greater than about 500 Å is essential to limit CPC intrusionand thus CPC loss to pores at the surfaces of the silica particles. Forinstance, where CPC and silica are slurried in a common aqueoussolution, the CPC is apt to intrude into silica surface pores havingsizes of greater than about 500 Å, but with much more difficulty intosmaller pore sizes. Therefore, it has been discovered that filling poreson the silica particles having sizes of greater than about 500 Åprovides silicas that are significantly more compatible with CPC.

Precipitated silica products prepared according to embodiments of thisinvention so as to reduce the cumulative surface area of all poreshaving sizes greater than about 500 Å to less than approximately 8 m²/g,generally have a % CPC Compatibility value of at least 55%, particularlygreater than 60%, and more particularly greater than 70%, and even moreparticularly greater than 80%, and it generally ranges between about 55%to about 95%. The “% CPC Compatibility” value of a silica is determinedby a testing procedure explained in the more detailed descriptionsprovided below. These % CPC Compatibility values are attainable due tothe treatment of the silica substrate particles effective to reduce thesurface pores having a size greater than about 500 Å such that thecumulative surface area of those sized pores generally is less thanapproximately 8 m²/g, and preferably less than approximately 7 m²/g, andmore preferably less than approximately 6 m²/g, as measured by mercuryintrusion porosimetry.

Dentifrices that contain this silica product offer the benefit that CPCalso can be used which remains at an effective antibacterial level inthe dentifrice despite the co-presence of silica abrasive. As anotherbenefit and advantage, dentifrices containing the silica product havesuperior flavor attributes. The flavor compatibility of the silicaproduct of this invention is superior to current commercial dental-gradesilica materials.

The oral cleaning compositions that can be benefited by incorporation ofthe silica product of embodiments of this invention include, forexample, dentifrices, chewing gums, and mouthwashes, and the like. Theterm “dentifrice” means oral care products in general such as, withoutintending to be limited, toothpastes, tooth powders, and denture creams.The silica particles of embodiments of the invention also have widercleaning utility and application, including, for instance, as a metal,ceramic or porcelain cleaning or scrubbing agent.

For purposes herein, the terminology “silica particles” means finelydivided silica, and the term encompasses silica primary particles,silica aggregates (i.e., unitary clusters of a plurality of silicaprimary particles), silica agglomerates (i.e., unitary clusters of aplurality of silica aggregates), singly or in combinations thereof. Theterm “denser”, as used in herein, refers to a lower porosity silicaparticulate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of cumulative surface area (m²/g) measured at variouspore sizes for a series of silicas representing embodiments of thisinvention and also comparison silicas represented by commercial silicasdetermined as described in examples herein.

FIG. 2 is plot of % CPC and cumulative pore area (m²/g) for pores withsizes greater than 500 Å, as measured from a series of silicas preparedas described in examples herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the preceding summary, the present invention isdirected to a unique silica product, which is particularly useful indentifrice compositions containing therapeutic agents, such as CPC. Thesilica product of embodiments of the present invention limits theability of CPC to bind to these products. Consequently, loss of CPC dueto inadvertent interaction with silica abrasive particles is minimized.

The silica product of an embodiment of this invention may be produced bya general process scheme, in which:

-   -   1) a slurry of amorphous silica particles is provided either by        slurrying up a prefabricated silica material obtained in dry        finely divided form, or, alternatively, from an ongoing        production run in which fresh precipitated silica is in slurry        or wet cake form without ever having been dried into powder        form, followed by;    -   2) precipitating active silica upon the substrate silica        particles effective to reduce the cumulative surface area of all        pores having sizes greater than about 500 Å to less than        approximately 8 m²/g, and preferably less than approximately 7        m²/g, and more preferably less than approximately 6 m²/g, as        measured by mercury intrusion porosimetry. The % CPC        Compatibility values of such surface-modified silica products is        at least 55%, particularly greater than 60%, and more        particularly greater than 70%, and even more particularly        greater than 80%, and generally ranges between about 55% to 95%.

It has been discovered that CPC compatibility, as measured according tothe technique set forth herein, is not related to the overall surfacearea of the silica, but, instead, it is directly related to thecumulative surface area of the pores having sizes greater thanapproximately 500 Å. In general, the greater the reduction of poreshaving sizes greater than approximately 500 Å in a silica product, thebetter the % CPC compatibility attained. Reducing the presence of poresizes less than about 500 Å does not significantly influence the CPCcompatibility achieved.

For purposes of measuring BET surface area, N₂ physisorption is commonlyused. However, because of the size of nitrogen gas, there are porescontributing to the overall surface area on silica particles that areaccessible to the gaseous N₂ used in conventional BET measurements, butwhich are not readily accessible to CPC. That is, surface area resultingfrom micropores may be accessible to gaseous nitrogen (as measured by N₂physisorption), but is not readily accessible to an aqueous slurry ofCPC in the time used to measure CPC compatibility as described herein.Consequently, it is not possible to use BET surface area measurementsper se to identify silica particles having the favorable pore sizedistributions described herein for obtaining % CPC Compatibility valuesof greater than approximately 55%. Instead, mercury intrusionporosimetery is used in embodiments of the present invention as themethod for measuring cumulative surface area of the silica particles atthe identified critical pore size values.

As generally known, the mercury porosimetry technique is based on theintrusion of mercury into a porous structure under stringentlycontrolled pressures. From the pressure versus intrusion data, theinstrument generates volume and size distributions using the Washburnequation. Since mercury does not wet most substances and will notspontaneously penetrate pores by capillary action, it must be forcedinto the pores by the application of external pressure. The requiredpressure is inversely proportional to the size of the pores, and onlyslight pressure is required to intrude mercury into large macroporeswhereas much greater pressures are required to force mercury intomicropores. Higher pressures are required to measure the pore sizes andsurface areas of the micropores present on the surfaces of silicaproducts of the present invention. Suitable instruments for measuringmicropore sizes and surface areas using mercury intrusion porosimetryfor purposes of the present invention is a Micromeritics® Autopore II9220 series automated mercury porosimeters, and the like.

Sourcing of Silica Substrate Particles

Regarding the silica particles provision of above general step 1),amorphous silica particles are provided. If provided in dry form, thedried crude silica used as the “particles” to be surface-modifiedaccording to this invention includes commercially obtainableprecipitated silicas, such as Zeodent® 113, Zeodent® 115, Zeodent® 153,Zeodent® 165, Zeodent® 623, Zeodent® 124 silicas, and so forth, whichare available from J.M. Huber Corporation. These commercially availablesilicas typically are in aggregate form.

The dry finely divided silica particles also may be obtained from asupply of premanufactured material made earlier at the same or differentproduction facility where procedures used for the surface area reductionstep can be performed at a later time.

The dry precipitated silicas to be used as the substrate particles forthe surface area reduction operation generally should have a medianparticle size of 1 to 100 μm, a BET specific surface area value ofapproximately 30 to 100 m²/g, and a linseed oil absorption ofapproximately 40 to 250 ml/100 g. Zeodent® 113, for example, typicallyhas a median particle size of approximately 10 μm, BET surface areavalue of approximately 80 m²/g, and a linseed oil absorption ofapproximately 85 ml/100 g. The silica particles used as the substratematerial for the coating operation, described below, preferably areconstituted of silica particles having a median diameter of 1 to 100micrometers. Substrate materials, such as high structure precipitatedsilica, silica gels and pyrogenic silica, with BET surface area greaterthan 100 m²/g, such as about 100 to 800 m²/g, or linseed oil absorptiongreater than 120 ml/100 g, such as about 120 to 400 ml/100 g, can beused in the present invention, although longer surface area reductiontimes (active silica deposition times) will be required to lower thesurface area to desired levels.

The dry precipitated silicas must be slurried in an aqueous mediumbefore they can be subjected to the dense silica coating applicationprocedure described herein. Generally, the dry silicas are slurried to asolids content that creates a pumpable mixture, generally of from about1 to about 50%.

Alternatively, crude undried liquid phase silica materials can beprepared in situ during a common production run scheme as the surfacearea reduction operation. Alternatively, a crude silica wet cake can bestored for later slurrying, or stored as a slurry thereof, until thesurface area reduction procedure is performed at a subsequent time,without ever drying the silica solids to powder form. The solids contentof the slurry provided before the surface area reduction operation isperformed will be the same as that described above in connection withthe dry silicas.

The liquid phase source of precipitated silicas generally should haveconstituent particle sizes, overall particle size, BET specific surfacearea value, and linseed oil absorption properties comparable to thoserespective values described above in connection with the dry source formof the silica. To the extent they meet those physical criteria, theliquid phase silicas can include amorphous precipitated silicas, silicagels or hydrogels, pyrogenic silica and colloidal silicas. In oneaspect, the silica particles provided in situ are in aggregate oragglomerate form.

The silicas can be produced by acidulating an alkali metal silicate witha mineral acid, such as sulfuric acid, or organic acid, with heating.Synthetic amorphous precipitated silicas are generally prepared byadmixing alkaline silicate solutions with acids with heating, stirring,and then filtering or centrifuging to isolate the precipitated silicasolids as a wet cake form thereof. The reaction media may optionallycontain an electrolyte, such as sodium sulfate. Wet cake of silicagenerally contains about 40 wt % to about 60 wt % water, and theremainder is principally solids. The precipitated reaction massgenerally is filtered and washed with water to reduce the Na₂SO₄ levelsto tolerable levels. Washing of the reaction product is generallyconducted after filtering. The pH of the washed wet cake can beadjusted, if necessary, prior to proceeding to subsequent stepsdescribed herein. If necessary, the washed wet cake is slurried to asolids content of between 1 to 50% before the surface area reductionprocedure is performed on it. As previously noted, if the silica isdried, or dried and comminuted to a desired size, it must be reslurriedbefore the surface area reduction procedure can be conducted on thecrude silica.

To the extent they meet other requirements discussed herein, the crudesilica to be used as a source of the substrate particles for particulartype of surface area reduction described herein can be, for example,precipitated silicas made as described in U.S. Pat. Nos. 4,122,161,5,279,815 and 5,676,932 to Wason et al., and U.S. Pat. Nos. 5,869,028and 5,981,421 to McGill et al., which teachings are incorporated hereinby reference.

Surface Area Reduction of Silica Substrate Particles

Regarding the surface area reduction of above general step 2) for poresizes larger than about 500 Å, after slurrying the crude silicaparticles in an aqueous medium, active silica is generated in the samemedium for a time period and under conditions sufficient to providedense amorphous silica deposits on the substrate particles sufficient toreduce the surface area and CPC's potential for binding to it. Ingeneral, the slurried crude silica particle intermediate product isdispersed in an aqueous medium in which active silica is generated byacidulating an alkali metal silicate with a mineral acid therein. Theresulting mixture is gently agitated or mixed, such as with a paddlemixer, for a sufficient period of time to ensure that the active silicaand substrate silica particles are substantially uniformly dispersed.The resulting silica product is filtered or otherwise dewatered, washed,and dried as needed.

In this regard, the methodology used to provide the active silica in themedium that is deposited as an amorphous silica material on the surfacesof the substrate particles generally involves similar chemistries andconditions applied to make the crude or substrate particles, except thatthe addition rates of the silicate and acid used for formation of activesilica must be sufficiently slowed in order to insure the active silicadeposits on the existing substrate silica particles and does not formseparate precipitated particles. The addition of active silica toorapidly will result in the formation of separate precipitated silicaparticles and will not result in the desired decrease in surface area ofthe substrate silica. It is desirable to use temperatures ranging from60 to 100° C., pH from 7 to 10, and an active silica deposition ratesuch that the specific surface area of the of the silica particlesmaterial is reduced. Optionally, a salt such as Na₂SO₄ can be added inan amount such that the desired decrease in surface area is stillobtained. Reaction temperatures of greater than 90° C. and pH greaterthan 9 are preferred for use during the surface area reduction portionof the process.

In one aspect, the surface area reduction process is manipulatedappropriately to ensure that the extent of deposition of active silicais at a rate and in an amount effective to provide a surface area, asmeasured by mercury intrusion, for pore sizes large than about 500 Å ofless than about 8 square meters per gram, preferably less than about 7square meters per gram, more preferably less than about 6 square metersper gram. It also should be in amount effective to reduce binding of CPCthereto as compared to the silica particles that has not been exposed toa surface area reduction process.

The precipitated silica product has a % CPC Compatibility valuegenerally of at least about 55%, particularly greater than 60%, moreparticularly greater than 70%, and can be even greater than 80%. The %CPC Compatibility value generally can range between about 55% to about95%. The “% CPC Compatibility” characteristic of the silica isdetermined by a testing procedure explained in the examples that follow.

The resulting silica also generally has a median particle size rangingbetween about 1 to about 100 microns, and preferably in one embodimentranges between about 5 and about 20 microns. The particle size of thesilicas is measured using a Horiba Particle Analyzer. Model LA-910manufactured by Horiba Instruments, Boothwyn, Pa.

The resulting silica product can be spray dried in a similar manner asthe treatment performed on the crude freshly prepared silicas.Alternatively, the wet cake obtained can be reslurried, and handled andsupplied in slurry form or supplied as a filter cake, directly.

Also, drying of silicas described herein can be effected by anyconventional equipment used for drying silica, e.g., spray drying,nozzle drying (e.g., tower or fountain), flash drying, rotary wheeldrying or oven/fluid bed drying. The dried silica product generallyshould have a 1 to 15 wt. % moisture level. The nature of the silicareaction product and the drying process both are known to affect thebulk density and liquid carrying capacity. Further, care must be takenthat the drying operation and subsequent operations do not detrimentallyaffect the structure of the silica obtained in the precipitation stage.The dried silica product is in a finely divided form. In one particularembodiment, the water content of the precipitated silica-containingfractions is about 25% by weight or more for all times until the dryingprocedure is performed on the silica product.

To decrease the size of the dried silica particles further, if desired,conventional grinding and milling equipment can be used. A hammer orpendulum mill may be used in one or multiple passes for comminuting andfine grinding can be performed by fluid energy or air-jet mill. Productsground to the desired size may be separated from other sizes byconventional separation techniques, e.g., cyclones, classifiers orvibrating screens of appropriate mesh sizing, and so forth.

There are also ways to reduce the particle size of the resulting silicaproduct before isolation and/or during the synthesis of the silicaproduct that affect the size of the dried product or product in slurryform. These include but are not limited to media milling, the use ofhigh shear equipment (e.g. high shear pump or rotor-stator mixers), orultrasound devices. Particle size reduction carried out on the wetsilica product can be done at anytime before drying, but more preferablyduring formation of the core and/or the deposition of the active silicaonto the core. Any particle size reduction done on the dry or wet silicaproduct should be done in a way not to significantly reduce the CPCcompatibility of the final product.

The recovery of the dried silica in the present invention does notrequire silica dewatering and dehydration to be performed with anorganic solvent replacement procedure. The isolation of the silicaproduct can be performed from an aqueous medium without occurrence ofproduct degradation.

Dentifrice Compositions

Dentifrices that contain the above-described silica product offer thebenefit that therapeutic agents, such as CPC also can be used whichremains at an effective antibacterial level in the dentifrice despitethe presence of silica abrasive. The silica particles show decreasedinteraction with CPC and as a result there remains an increase in thefree CPC in the dentifrice available to improve antibacterial efficacy.

While CPC is used herein as representative of dentifrice therapeuticagents, other antimicrobial agents, (cationic, anionic and nonionic) arecontemplated by the invention. Other suitable antimicrobial agentsinclude bisguanides, such as alexidine, chlorhexidine and chlorhexidinegluconate; quarternary ammonium compounds, such as benzalkonium chloride(BZK), benzethonium chloride (BZT), cetylpyridinium chloride (CPC), andDomiphen bromide; metal salts, such as zinc citrate zinc chloride, andstannous fluoride; sanguinaria extract and sanguinarine; volatile oils,such as eucalyptol, menthol, thymol, and methyl salicylate; aminefluorides; peroxides and the like. Therapeutic agents may be used indentifrice formulations singly or in combination.

As another benefit and advantage, dentifrices containing the silicaproduct have a superior flavor attributes. Dentifrice compositionsincorporating the silica product described herein generally contain thesilica in an effective amount for abrasive and polishing action. Thisamount can vary, depending on other ingredients of the formulation, forexample, but generally will range from about 5 to about 60 wt %.

Dentifrice compositions incorporating the silica product describedherein preferably also contain CPC in an antimicrobial effective amount.This amount can vary, depending on other ingredients of the formulationand limitations placed upon its use by regulating authorities (e.g.FDA), for example, but generally will range from about 0.01 to about 1wt %., preferably from about 0.1 to about 0.75 wt. %, most preferablyfrom about 0.25 to 0.50 wt. %.

Other additives commonly used or otherwise beneficial in dentifricesalso optionally may be included in the formulation. A pharmaceuticallyacceptable carrier for the components of dentifrice compositionscontaining the silica product of the present invention is optional andcan be any dentifrice vehicle suitable for use in the oral cavity. Suchcarriers include the usual components of toothpastes, tooth powders,prophylaxis pastes, lozenges, gums, and the like and are more fullydescribed thereafter.

Flavoring agents optionally can be added to dentifrice compositions.Suitable flavoring agents include oil of Wintergreen, oil of peppermint,oil of spearmint, oil of sassafras, and oil of clove, cinnamon,anethole, menthol, and other such flavor compounds to add fruit notes,spice notes, etc. These flavoring agents consist chemically of mixturesof aldehydes, ketones, esters, phenols, acids, and aliphatic, aromaticand other alcohols.

Sweetening agents, which can be used, include aspartame, acesulfame,saccharin, dextrose, levulose and sodium cyclamate. Flavoring andsweetening agents are generally used in dentifrices at levels of fromabout 0.005% to about 2% by weight

A water-soluble fluoride compound optionally can be added and present indentifrices and other oral compositions in an amount sufficient to givea fluoride ion concentration in the composition at 25° C., and/or whenit is used of from about 0.0025% to about 5.0% by weight, preferablyfrom about 0.005% to about 2.0% by weight, to provide additionalanticaries effectiveness. A wide variety of fluoride ion-yieldingmaterials can be employed as sources of soluble fluoride in the presentcompositions. Examples of suitable fluoride ion-yielding materials arefound in U.S. Pat. Nos. 3,535,421, and 3,678,154, both beingincorporated herein by reference. Representative fluoride ion sourcesinclude: stannous fluoride, sodium fluoride, potassium fluoride, sodiummonofluorophosphate and many others. Stannous fluoride and sodiumfluoride are particularly preferred, as well as mixtures thereof.

Water is also present in the toothpastes and dentifrices according toanother embodiment of this invention. Water employed in the preparationof suitable toothpastes should preferably be deionized and free oforganic impurities. Water generally comprises from about 2% to 50%,preferably from about 5% to 20%, by weight, of the toothpastecompositions. These amounts of water include the free water which isadded plus that which is introduced with other additives and materials,such as humectant.

In preparing toothpastes, it often is necessary to add some thickeningor binder material to provide a desirable consistency and thixotropy.Preferred thickening agents are carboxyvinyl polymers, carrageenan,hydroxyethyl cellulose and water-soluble salts of cellulose ethers suchas sodium carboxymethyl cellulose and sodium carboxymethyl hydroxyethylcellulose. Natural gums such as gum karaya, xanthan gun, gum arabic, andgum tragacanth can also be used. Thickening agents in an amount fromabout 0.5% to about 5.0% by weight of the total composition generallycan be used.

Silica thickeners can also be used to modify toothpaste rheology.Precipitated silica, silica gels and fumed silica can be used. Silicathickeners can be added generally at a level of about 5% to about 15%.

It is also often desirable to include some humectant material in atoothpaste to keep it from hardening. Suitable humectants includeglycerin (glycerol), sorbitol, polyalkylene glycols such as polyethyleneglycol and polypropylene glycol, hydrogenated starch hydrolyzates,xylitol, lactitol, hydrogenated corn syrup, and other edible polyhydricalcohols, used singly or as mixtures thereof. Suitable humectants can beadded generally at a level of from about 15% to about 70%.

Chelating agents optionally can be added to the dentifrices of theinvention, such as alkali metal salts of tartaric acid and citric acid,or alkali metal salts of pyrophosphates or polyphosphates.

Other optional ingredients and adjuvants of dentifrices, such as thosedescribed in U.S. Pat. No. 5,676,932 and Pader, M., Oral HygieneProducts and Practice, Marcel Dekker, Inc., New York, 1988, forinstance, also can be added as needed or desired. These other optionaladjuvants, additives, and materials that can be added to the dentifricecompositions of the present invention include, for example, foamingagents (e.g., sodium lauryl sulfate), detergents or surfactants,coloring or whitening agents (e.g., titanium dioxide, FD&C dyes),preservatives (e.g., sodium benzoate, methyl paraben), chelating agents,antimicrobial agents, and other materials that can be used in dentifricecompositions. The optional additives, if present, generally are presentin small amounts, such as no greater than about 6% by weight each.

In all cases, the ingredients used in dentifrice formulations, such asthickening gums, foaming agents, etc., are selected to be compatiblewith the therapeutic agents and flavors.

Additionally, while the usefulness of the abrasive cleaning material ofthis invention is specifically illustrated in oral cleaningcompositions, it is will be appreciated that the silica of thisinvention has wider usefulness. For instance, it can be used in metal,ceramic or porcelain cleaning or scrubbing and as a CMP (ChemicalMechanical Planarization) polishing agent.

EXAMPLES

The following examples are presented to illustrate the invention, butthe invention is not to be considered as limited thereto. In thefollowing examples, parts are by weight unless indicated otherwise.

In the following examples, a series of silica products were preparedwith varied surface treatments to investigate possible relationshipsbetween cumulative surface areas provided for various pore size valuesand the CPC compatibility attained for the silica products. Severalcommercially available silica products also were analyzed for sake ofcomparison.

Preparation of Silica Substrate Particles

For the following Examples 1-3 and Comparative Examples 1-2, the silicasubstrates used were portions of a bead-milled silica wet cake that wasprepared in the following manner.

1900 liters of sodium silicate solution (13%, 2.50 M.R.) was added to astainless steel reactor and was heated to 85° C. with stirring. Sodiumsilicate (13%, 2.50 molar ratio (M.R.)) and sulfuric acid (11.4%) weresimultaneously added to the reactor at rates of 387.5 and 170.3 LPM,respectively, for 48 minutes. After 48 minutes, the flow of silicate tothe reactor was stopped and the pH was adjusted to 5.0 to 5.2 with thecontinued addition of sulfuric acid (11.4%). The reaction mixture wasthen digested for 10 minutes at 93° C. Silica wet cake was recoveredfrom the reaction mixture.

The silica wetcake was bead milled in the following manner. A Cobal®Mill MS-50 Machine # 74996/00 manufactured by Romaco AG, Frymakoruma,was used for the bead mill processing. 7 liters of 2.0-2.5 mm ZirconiumOxide beads by SEPR were used as the charge for milling media. Thesilica wetcake was diluted with water to provide a pumpable slurry(31.8% solids) which was fed at a rate 2.0 liters per minute to theCobal® Mill. The silica slurry was bead milled to a top particle size ofapproximately 35 μm.

Preparation of Surface-Coated Silica Particles

Example 1

63 L of bead milled silica substrate particles (˜33.55 % solids) wereadded to a 400 gallon reactor along with 265 L of water. The slurry washeated to 95° C. with stirring at 78 RPM. Once a temperature of 95° C.was reached, sodium silicate (13.3%, 2.65 M.R. pre-heated to 90° C.,1.123 g/ml S.G.) was added at 3.6 L/min until pH 9.5 was reached. Once apH of 9.5 was reached, sulfuric acid (11.4%) was added at ˜1.9 L/min inorder to maintain this pH. If necessary, the acid flow rate was adjustedto maintain pH 9.5. After 150 minutes, the silicate flow was stopped andthe pH was adjusted to 5.0 with the addition of sulfuric acid at 3.8L/min. Once a pH of 5.0 was reached, the flow of acid was stopped andthis pH was maintained for a period of 10 minutes. The reaction mixturewas then filtered, washed with water until a conductivity of <1500 μS,and then spray dried.

Example 2

43 L of bead milled silica substrate particles (˜33.55 % solids) wereadded to a 400 gallon reactor along with 180 L of water. The slurry washeated to 95° C. with stirring at 78 RPM. Once a temperature of 95° C.was reached, sodium silicate (13.3%, 2.65 M.R., pre-heated to 90° C.,1.123 g/ml S.G.) was added at 4.7 L/min until a pH of 9.5 was reached.Once a pH of 9.5 was reached, sulfuric acid (11.4%) was added at ˜2.2L/min in order to maintain this pH. If necessary, the acid flow rate wasadjusted to maintain a pH of 9.5. After 30 minutes the flow of silicatewas adjusted to 4.5 L/min and the flow of acid to ˜2.2 L/min. After 60minutes the flow of silicate was adjusted to 4.2 L/min and the flow ofacid to ˜2.0 L/min. After 90 minutes the flow of silicate was adjustedto 3.6 L/min and the flow of acid to ˜1.7 L/min. After 120 minutes theflow of silicate was adjusted to 3.1 L/min and the flow of acid to ˜1.5L/min. After 150 minutes, the silicate flow was stopped and the pH wasadjusted to 5.0 with the addition of sulfuric acid at 3.8 L/min. Once pH5.0 was reached, the flow of acid was stopped and this pH was maintainedfor a period of 10 minutes. The reaction mixture was then filtered,washed with water until a conductivity of <1500 μS, and then spraydried.

Example 3

33 L of bead milled silica substrate particles (˜33.55% solids) wereadded to a 400 gallon reactor along with 138 L of water. The slurry washeated to 95° C. with stirring at 78 RPM. Once a temperature of 95° C.was reached, sodium silicate (13.3%, 2.65 M.R., pre-heated to 90° C.,1.123 g/ml S.G.) was added at 5.1 L/min until a pH of 9.5 was reached.Once a pH of 9.5 was reached, sulfuric acid (11.4%) was added at ˜2.4L/min in order to maintain this pH. If necessary, the acid flow rate wasadjusted to maintain a pH of 9.5. After 30 minutes the flow of silicatewas adjusted to 4.9 L/min and the flow of acid to ˜2.3 L/min. After 60minutes the flow of silicate was adjusted to 4.5 L/min and the flow ofacid to ˜2.2 L/min. After 90 minutes the flow of silicate was adjustedto 4.0 L/min and the flow of acid to ˜1.9 L/min. After 120 minutes theflow of silicate was adjusted to 3.5 L/min and the flow of acid to ˜1.7L/min. After 150 minutes, the silicate flow was stopped and the pH wasadjusted to 5.0 with the addition of sulfuric acid at 3.8 L/min. Once pH5.0 was reached, the flow of acid was stopped and this pH was maintainedfor a period of 10 minutes. The reaction mixture was then filtered,washed with water until a conductivity of <1500 μS, and then spraydried.

Comparative Example 1

113 L of bead milled silica substrate particles (˜33.55% solids) wereadded to a 400 gallon reactor along with 460 L of water. The slurry washeated to 95° C. with stirring at 78 RPM. Once a temperature of 95° C.was reached, sodium silicate (13.3%, 2.65 M.R., pre-heated to 90° C.,1.123 g/ml S.G.) was added at 2.4 L/min until pH 9.5 was reached. Once apH of 9.5 was reached, sulfuric acid (11.4%) was added at ˜1.3 L/min inorder to maintain this pH. If necessary, the acid flow rate was adjustedto maintain a pH of 9.5. After 150 minutes, the silicate flow wasstopped and the pH was adjusted to 5.0 with the addition of sulfuricacid at 3.8 L/min. Once a pH of 5.0 was reached, the flow of acid wasstopped and this pH was maintained for a period of 10 minutes. Thereaction mixture was then filtered, washed with water until aconductivity of <1500 μS, and then spray dried.

Comparative Example 2

90 L of bead milled silica substrate particles (˜33.55% solids) wereadded to a 400 gallon reactor along with 360 L of water. The reactionmixture was heated to 95° C. with stirring at 78 RPM. Once a temperatureof 95° C. was reached, sodium silicate (13.3%, 2.65 M.R., pre-heated to90° C., 1.123 g/ml S.G.) was added at 3.3 L/min until a pH of 9.5 wasreached. Once a pH of 9.5 was reached, sulfuric acid (11.4%) was addedat 1.7 L/min in order to maintain this pH. If necessary, the acid flowrate was adjusted to maintain a pH of 9.5. After 150 minutes, thesilicate flow was stopped and the pH was adjusted to 5.0 with theaddition of sulfuric acid at 3.8 L/min. Once pH 5.0 was reached, theflow of acid was stopped and this pH was maintained for a period of 10minutes. The reaction mixture was then filtered, washed with water untila conductivity of <1500 μS, and then spray dried.

For Examples 1-3 and Comparative Examples 1-2, as well as any otherexamples summarized herein, the “% CPC Compatibility” value wasdetermined in the following manner.

“% CPC Compatibility” Test

27.00 g of a 0.3% solution of CPC was added to a 3.00 g sample of thesilica to be tested. The silica was previously dried at 105° C. to 150°C. to a moisture content of 2% or less, and the pH of the sample wasmeasured to ensure the 5% pH was between 5.5 and 7.5. The mixture wasshaken for a period of 10 minutes. Accelerated aging testing requiresagitation of the test specimen for 1 week at 140° C. After agitation wascomplete, the sample was centrifuged and 5 ml of the supernatant waspassed through a 0.45 μm PTFE milli-pore filter and discarded. Anadditional 2.00 g of supernatant was then passed through the same 0.45μm PTFE milli-pore filter and then added to a vial containing 38.00 g ofdistilled water. After mixing, an aliquot of the sample was placed in acuvette (methyl methacrylate) and the U.V. absorbance was measured at268 nm. Water was used as a blank. The % CPC Compatibility wasdetermined by expressing as a percentage the absorbance of the sample tothat of a CPC standard solution prepared by this procedure with theexception that no silica was added.

% Active Silica Deposited

A “% Active Silica Deposited” was determined for silica products bycalculation from the batch parameters. Active silica is determined byknowing the volume of active silica used and the silicate concentration,specific gravity (S.G.) and molar ratio (M.R.). Likewise, the totalbatch silica is calculated by knowing the total volume of silica usedand silicate concentration, S.G. and M.R. % active silica depositedequals g active silica divided by g total batch silica times 100. Allterms except the volumes cancel so that the % active silica depositedequals the active silica volume/total silica volume. When starting witha premanufactured silica substrate, which is measured in weight values,one must use the above equation to convert active silica to a weightmeasure, such as grams to put all ingredients on the same basis.

Table 1 below is a summary of the CPC compatibility and % active silicadeposited for the silicas produced in the preceding examples andcomparison examples.

TABLE 1 % Active Silica % CPC Sample Deposited Compatibility CE1 45 14.7CE2 60 43.9 1 70 66.7 2 80 76.6 3 85 76.8

In Table 2 below, a summary of the physical properties of the CPCcompatible silica samples produced by the preceding examples is setforth. Median particle size was measured using a Microtrac II apparatus,made by Leeds and Northrup. The BET and linseed oil absorptionproperties were measured in the respective manners described in commonlyassigned U.S. Pat. No. 5,981,421, which descriptions are incorporatedherein by reference. The % 5 pH values of the silicas (i.e., a 5 weight% silica slurry) were measured by a conventional pH sensitive electrode.CTAB external surface area of silica is determined by absorption of CTAB(cetyltrimethylammonium bromide) on the silica surface, the excessseparated by centrifugation and determined by titration with sodiumlauryl sulfate using a surfactant electrode. The external surface of thesilica is determined from the quantity of CTAB adsorbed (analysis ofCTAB before and after adsorption). Specifically, about 0.5 g of silicais placed in a 250-ml beaker with 100.00 ml CTAB solution (5.5 g/L),mixed on an electric stir plate for 1 hour, then centrifuged for 30minutes at 10,000 rpm. One ml of 10% Triton X-100 is added to 5 ml ofthe clear supernatant in a 100-ml beaker. The pH is adjusted to 3.0-3.5with 0.1 N HCI and the specimen is titrated with 0.0100 M sodium laurylsulfate using a surfactant electrode (Brinkmann SURl5Ol -DL) todetermine the endpoint.

TABLE 2 Median Oil particle CTAB BET Absorption 5% size Sample (m²/g)(m²/g) (cc/100 g) pH (μm) CE1 10 24 78 7.36 3.8 CE2 7 19 90 6.68 5.1 1 32 78 6.82 5.9 2 1 6 58 6.79 6.7 3 1 9 58 6.27 7.0

Example 4

In this example, the silica was precipitated, and comminuted, at thereaction vessel in the following manner. 40 L of sodium silicate (13%,3.32 M.R., 1.112 g/ml S.G.) was added to a 400-gallon reactor and washeated to 95° C. with stirring at 50 RPM. Once the temperaturestabilized at 95° C., a Silverson in-line mixer coupled to the reactorby a re-circulation line was set to 100 Hz with re-circulation of 100Hz. Sodium silicate (13%, 3.32 M.R., pre-heated to 90° C., 1.112 g/mlS.G.) and sulfuric acid (11.4%) were then simultaneously added to thereactor at rates of 7.8 L/min and 2.3 L/min, respectively, for 47minutes. After 15 minutes, the stir rate was increased to 75 RPM. After47 minutes, the Silverson in-line mixer was stopped. Sodium silicateaddition was adjusted to 2.2 L/min and the pH was adjusted to 9.5+/−0.2with continued addition of sulfuric acid (11.4%). Once the pH reached9.5, sulfuric acid (11.4%) was added a rate of ˜0.7 L/min. If necessary,the acid rate was adjusted to maintain pH 9.5+/−0.2. After 197 minutes(total), the flow of sodium silicate was stopped and the pH was adjustedto 5.0 with the addition of sulfuric acid (11.4%) at 2.3 L/min. Thebatch was digested for 10 minutes at pH 5.0, was filtered, washed toconductivity <1500 μS, and spray dried. The silica product obtained hada % CPC Compatibility value of 81.5.

The silica product obtained also had the physical properties indicatedin Table 3.

TABLE 3 Median CTAB BET Oil Particle Sample (m²/g) (m²/g) (ml/100 g) %H2O 5% pH Size (μm) 4 7 11 28 5.46 7.12 12.7

For comparison purposes, the physical properties were measured on acommercial silica product sold as Sorbosil AC33 by INEOS, which aresummarized in Table 4.

TABLE 4 % CPC Sample CTAB (m²/g) BET (m²/g) Compatibility Sorbosil AC3315 218 46.0Characterization of Silica by Hg Intrusion Porosimetry

Hg intrusion porosimetry analyses was performed as follows on the silicasamples prepared in these examples, and on comparative example 1 andseveral commercially available silicas including Sorbosil AC33 andZeodent® 105.

The total pore volume (Hg) for these silica samples was measured at aseries of different pore diameter ranges by mercury porosimetry using aMicromeritics Autopore II 9220 apparatus. The pore diameters can becalculated by the Washburn equation employing a contact angle Theta (θ)equal to 130° and a surface tension gamma equal to 484 dynes/cm. Thisinstrument measures the void volume and pore size distribution ofvarious materials. Mercury is forced into the voids as a function ofpressure and the volume of the mercury intruded per gram of sample iscalculated at each pressure setting. Total pore volume expressed hereinrepresents the cumulative volume of mercury intruded at pressures fromvacuum to 60,000 psi.

Increments in volume (cm³/g) at each pressure setting are plottedagainst the pore radius or diameter corresponding to the pressuresetting increments. The peak in the intruded volume versus pore radiusor diameter curve corresponds to the mode in the pore size distributionand identifies the most common pore size in the sample. Specifically,sample size is adjusted to achieve a stem volume of 30-50% in a powderpenetrometer with a 5 ml bulb and a stem volume of about 1.1 ml. Samplesare evacuated to a pressure of 50 μm of Hg and held for 5 minutes.Mercury fills the pores from 1.5 to 60,000 psi with a 10 secondequilibrium time at each of approximately 150 data collection points.

Hg intrusion porosimetry gave information about pores from approximately100 Å to those over 1 μm in size. In comparison, N₂ physisorption (BET)gives information from pores approximately 5 to 1000 Å in size.

The cumulative pore area for different ranges of pore diameters is shownin the Table 5 below. Total cumulative pore area is the total pore areameasured by mercury intrusion. Cumulative pore areas for the differentranges are described as the pore area from the specified pore size andup. For example, “>50 Å” means the cumulative pore area in m²/g forpores having an average pore diameter of 50 angstroms and greater.

TABLE 5 Cumulative Pore Area (m2/g) Sample % CPC Legend Total >50 Å >100Å >200 Å >300 Å >400 Å >500 Å >600 Å Example 1 66.7 ▴ 84.42 44.23 18.329.54 7.30 6.40 5.70 5.37 Example 2 76.6 ▪ 88.78 41.18 16.03 7.62 5.504.57 4.05 3.77 Example 3 76.8 □ 55.81 27.72 11.60 6.19 4.69 3.97 3.533.28 Example 4 81.5 ● 69.08 34.60 13.00 5.41 3.41 2.66 2.13 1.92Comparative 14.7 ◯ 116.2 65.6 33.2 20.58 16.16 13.89 12.01 11.02 Example1 Sorbosil 46 ♦ 111.80 75.26 45.18 26.96 18.94 14.77 11.26 9.48 AC 33Zeodent 105 <5 — 73.11 47.70 44.81 28.56 20.15 15.30 12.60 10.01

By plotting the cumulative surface area values as a function of porediameter, a graphical representation of the data can be seen in FIG. 1.The cumulative surface area data is listed in Table 5 for each silicasample along with the symbol corresponding to each plot in FIG. 1 asapplicable. FIG. 2 is a plot showing the correlation of the pore areafor pores greater than 500 angstroms and CPC compatibility. Example 4was replicated 9 times providing the cluster of data points shown onFIG. 2 illustrating reproducibility. When the cumulative pore area forpores greater than 500 Å was plotted versus CPC compatibility as in FIG.2, a strong correlation was observed (R² values>90%). It can be seenfrom the surface area plots in FIGS. 1 and 2 for the different silicasamples that the cumulative surface area (from pores greater than 500 Å)needs to be less than ˜8 m²/g to obtain CPC compatibility values greaterthan ˜55%.

It will be understood that various changes in the details, materials,and arrangements of the parts which have been described and illustratedherein in order to explain the nature of this invention may be made bythose skilled in the art without departing from the principles and scopeof the invention as expressed in the following claims.

1. Precipitated silica comprising silica product particles having aporous surface, the silica particles having a cumulative surface areafor all pores having diameters greater than about 500 Å of less than 8m²/g, as measured by mercury intrusion, a BET specific surface area ofless than approximately 30 square meters per gram, and a percentagecetylpyridinium chloride (% CPC) Compatibility of greater than about55%.
 2. A silica product according to claim 1, wherein the silicaparticles have a percentage cetylpyridinium chloride (% CPC)Compatibility of greater than approximately 60%.
 3. A silica productaccording to claim 1, wherein the silica particles have a % CPCCompatibility of greater than approximately 70%.
 4. A silica productaccording to claim 1, wherein the silica particles have a % CPCCompatibility of greater than approximately 80%.
 5. A silica productaccording to claim 1, wherein the silica particles have a mediandiameter of 1 to 20 micrometers.
 6. A silica product according to claim1, wherein the silica particles have a % CPC Compatibility value ofapproximately 55% to 95%.
 7. A silica product according to claim 1,wherein the silica particles comprise silica aggregates or agglomeratesindividually comprising unitary clusters of a plurality of silicaprimary particles.
 8. A silica product according to claim 1, the silicaparticles having a cumulative surface area for all pores havingdiameters greater than about 500 Å of less than 7 m²/g, as measured bymercury intrusion.
 9. Dentifrice, comprising: a silica productcomprising silica particles having a porous surface, the silicaparticles having a cumulative surface area for all pores havingdiameters greater than about 500 Å of less than 8 m²/g, as measured bymercury intrusion, a BET specific surface area of less thanapproximately 30 square meters per gram, and a percentagecetylpyridinium chloride (% CPC) Compatibility of greater than about55%.
 10. Dentifrice according to claim 9, wherein the silica particleshave a percentage cetylpyridinium chloride (% CPC) Compatibility ofgreater than approximately 60%.
 11. Dentifrice according to claim 9,wherein the silica particles provide an increased flavor compatibilityas compared to a dentifrice containing corresponding silica particleswithout said cumulative surface area and % CPC Compatibility. 12.Dentifrice according to claim 9, wherein the silica particles have apercentage cetylpyridinium chloride (% CPC) Compatibility of greaterthan approximately 70%.
 13. Dentifrice according to claim 9, wherein thesilica particles have a percentage cetylpyridinium chloride (% CPC)Compatibility of greater than approximately 80%.
 14. Dentifriceaccording to claim 9, wherein the silica wherein the silica particleshave a % CPC Compatibility value of approximately 55% to 95%. 15.Dentifrice according to claim 9, wherein the silica particles compriseaggregates or agglomerates individually comprised of clusters of aplurality of silica primary particles.
 16. Dentifrice according to claim9, further including an effective amount of at least one flavorantcompatible with CPC.
 17. Dentifrice according to claim 9, furtherincluding an effective amount of an anticaries compound comprising afluoride ion source.
 18. Dentifrice according to claim 9, furtherincluding an effective amount of antimicrobial agent.
 19. Dentifriceaccording to claim 9, the silica particles having a cumulative surfacearea for all pores having diameters greater than about 500 A of lessthan 7 m²/g, as measured by mercury intrusion.
 20. Dentifrice,comprising: a) antibacterial effective amount of cetylpyridiniumchloride; b) precipitated silica product comprising silica particleshaving a porous surface, the silica particles having a cumulativesurface area for all pores having diameters greater than about 500 Å ofless than 8 m²/g, as measured by mercury intrusion, a BET specificsurface area of less than approximately 30 square meters per gram, and apercentage cetylpyridinium chloride (% CPC) Compatibility of greaterthan about 55%.
 21. Process for making precipitated silica product,comprising: a) providing amorphous silica substrate particles having amedian diameter of 1 to 100 micrometers; b) depositing active silicaonto surfaces of the silica substrate particles by acidulation of analkali metal silicate in an aqueous medium, in which the substrateparticles are dispersed, in an amount effective to provide a slurry ofsilica particles having a porous surface, the silica particles having acumulative surface area for all pores having diameters greater thanabout 500 A of less than 8 m²/g, as measured by mercury intrusion, and apercentage cetylpyridinium chloride (% CPC) Compatibility of greaterthan about 55%.
 22. The process of claim 21, further comprisingdewatering and drying the silica particles to a flowable finely dividedparticulate form.
 23. The process of claim 21, wherein the providing ofthe silica particles comprises slurrying a dry flowable particulate formof the silica particles in an aqueous solution.
 24. The process of claim21, wherein the providing of the silica particles comprises forming thesilica particles in situ by acidulation of an alkali metal silicate inan aqueous medium without drying below 20% water content beforeinitiating step “b” thereof.
 25. The process of claim 21, wherein theproviding of the silica particles comprises providing silica aggregatesor agglomerates individually comprising unitary clusters of a pluralityof the amorphous silica primary particles.
 26. The process of claim 21,wherein the silica particles have a % CPC Compatibility of greater thanapproximately 60%.
 27. The process of claim 21, wherein the silicaparticles have a % CPC Compatibility of greater than approximately 70%.28. The process of claim 21, wherein the silica particles have a % CPCCompatibility of greater than approximately 80%.
 29. The process ofclaim 21, wherein the silica particles have a % CPC Compatibility withinthe range of about 55% to about 90%.
 30. The product of the process ofclaim 21.